1. Field of the Invention
The invention relates to protection circuits for motors, such as compressor motors for refrigeration or air conditioning systems; and particularly to a protection circuit responsive to a condition, such as a loss of a lubricating oil pressure for more than a predetermined duration, for stopping the operation of the motor.
2. Description of the Prior Art
The prior art, as exemplified in U.S. Pat. Nos. 3,290,576, 3,599,439, 3,673,811, 3,753,043, and 3,787,793, contains a number of motor protection circuits which are responsive to loss of lubricating oil pressure for more than a predetermined duration to stop a motor. U.S. Pat. No. 3,848,211 discloses a latching electrical switch construction. The prior art also contains a variety of motor protection circuits, timing circuits or control circuits such as are described in U.S. Pat. Nos. 3,102,677, 3,435,298, 3,638,091, 3,648,074, 3,652,916, 3,681,671, 3,688,130, 3,694,669, 3,712,991, 3,716,756, 3,749,992, 3,769,529, 3,796,061 and 3,801,889. The prior art motor controls have one or more deficiencies such as being excessively costly, not being usable on different voltage supplies, being restricted to a limited sequence of motor controls, being relatively unreliable, not being readily adjustable when installed, etc.